1. Field of the Invention
This invention relates to the selection and control of the output of a pressure compensated pump during operation. More particularly, it relates to the introduction of a digitally selected reference pressure for the selection and control of the pump output.
2. Description of the Related Art
U.S. Pat. No. 2,999,482, entitled "Digital Fluid Control System" issued to J. L. Bower discloses a system in which a digitally coded signal is caused to provide a plurality of fluid signals individually proportional to the digits of such coded signal and means are provided for combining these fluid signals to provide an analog fluid signal indicative of the number represented by the original digitally coded signal.
The Bower device is limited in that it is sensitive to variation in load at the actuator, and thus cannot be accurate. Its end objective is a velocity of actuator stroking. System pressure will immediately jump to pump relief valve pressure when the actuator reaches the end of its stroke. As shown, the whole system is dedicated to one load (actuator). Duplication is required for each load.
Furthermore, successful application of the Bower device requires tremendous excess hydraulic power capability compared to the load, and only one load. This capability does not exist in aircraft.
U.S. Pat. No. 3,164,065, entitled "Incremental Digital Fluid Actuator", issued to the present inventor, discloses a position commanding/sensing device with the hydraulic equivalent of a potentiometer and closed loop on positon. An orifice is digitally selected and .DELTA.P is thus generated. A contoured valve is connected to the actuator so that it generates an area proportional to the actuator stroke. Both .DELTA.P's are matched and a servo-valve parts flow so that the actuator .DELTA.P matches the selected .DELTA.P.